Filament wound vessel



Dec. 30, 1969 c. RAGETTLI 3,486,655

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ATTORNEYS United States Patent 3,486,655 FILAMENT WOUND VESSEL Christian Ragettli, Zurich, Switzerland, assignor to Metal Containers Limited, London, England, a company of the United Kingdom Filed Apr. 3, 1967, Ser. No. 629,058 Claims priority, application Great Britain, Apr. 1, 1966, 14,517/66 Int. 'Cl. B31c 9/00 U.S. 01. 2203 3 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a filament wound vessel and, more particularly, to the method for winding the filaments to form a filament wound vessel having improved strength characteristics.

When forming a filament wound vessel, it is necessary to wind the individual strands that are composed of syn thetic resin-impregnated filaments or the ribbons which are composed of a plurality of such strands formed in a coplanar relationship in a number of layers so that the vessel that is formed has the desired wall thickness as well as being gas and liquid tight. It has been heretofore the practice to form a filament wound vessel by using a mandrel having an exterior surface generally corresponding to the desired shape of the vessel. The strands or ribbons are generally passed through a stage in which they are impregnated with a synthetic resin and are then passed to the winding machine. Typically, the winding machine has a carriage which traverses the longitudinal length of the mandrel while winding the strands or ribbons about the mandrel which is being rotated. Initially, the leading end of the strands or ribbons is attached in some manner to the mandrel and the carriage begins traversing the longitudinal dimension of the mandrel and winding the strands or ribbons about the mandrel in a predetermined configuration. One method includes wrapping the strands or ribbons transversely about the mandrel substantially in the form of circles. The number of layers applied is continued until the desired thickness of the wall of the filament wound vessel has been reached. The vessel is generally formed in such a manner that one of the poles located at the longitudinal ends of the vessel has a large polar opening so that the mandrel can be removed from the interior of the vessel. The polar opening can then be closed by inserting a fitting therein.

In forming a filament Wound vessel it has been found that greatly improved strength characteristics can be achieved by winding the strands or ribbons in a manner other than merely transversely about the mandrel. While the strength characteristics have been increased, filament wound vessels formed by windings other than transverse often develop localized weakened areas that affect the burst strength of the vessel.

A general aim of the invention is the provision of a filament wound vessel that is characterized by its gas and liquid tightness and its improved burst strength.

A more specific object is to provide a filament wound vessel and a method for its manufacture in which excessive bending stresses in the filaments that would cause buckling and/or fracture of the strands are prevented.

Other objects and advantages of the invention will become apparent as the following description proceeds, taken in conjunction with the accompanying diagrammatic drawings in which:

FIGURE 1 is a side elevation view of a filament wound vessel in which there is illustrated a single strand of a substantially longitudinal winding that has been designated as Type I;

FIG. 2 is a bottom plan view of the filament wound vessel shown in FIGURE 1 completing the illustration of the Type I winding;

FIG. 3 is a side elevation view of a filament wound vessel-showing a single winding of a transverse winding designated as Type II;

FIG. 4 is a bottom plan view of the filament wound vessel shown in FIGURE 3;

FIG. 5 is a side elevation view of a filament wound ves sel exhibiting a single strand of a layer in a substantially longitudinal winding designated as Type III;

FIG. 6 is a bottom plan view of the filament wound vessel shown in FIGURE 5 and completing the illustration of the Type III winding;

FIG. 7 is a side elevation view of a filament wound vessel illustrating a single winding of a transverse winding designated as Type IV;

FIG. 8 is a bottom plan view of the filament wound vessel illustrated in FIGURE 7;

FIG. 9 is a side elevation view of a filament wound vessel showing a single winding of a strand that forms a transition between longitudinal and transverse windings and has been designated as Type V;

FIG. 10 is a bottom plan view of the filament wound vessel illustrated in FIGURE 9 completing the illustion of the Type V winding;

FIG. 11 is a side elevation view of a filament wound vessel illustrating a single winding of a transverse winding which has been designated Type VI;

FIG. 12 is a bottom plan view of the filament wound vessel illustrated in FIGURE 11;

FIGURE 13 is a side elevation view of a filament wound vessel having thereon a substantially longitudinal winding as illustrated in FIGURE 1 and a transverse winding as illustrated in FIGURE 3; and

FIGURE 14 is a bottom plan view of the filament wound vessel shown in FIGURE 13.

While the invention is susceptible of various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail.

The composition of the filaments that are used to form either the strands or ribbons to be used as the windings do not form a part of this invention and can suitably be of any materials that have been used for this purpose. Glass has been found to be a suitable material. Similarly, the composition of the synthetic resin that is used to impregnate the strands is not a critical feature of the invention and conventionally used resins such as an epoxy resin may be employed. To form the filament woundwessel of this invention the strands or ribbons that are to be wound can be impregnated with synthetic resin by any conventional means. The synthetic resin-impregnated strands or ribbons are then forwarded to any conventional winding machine having a carriage that traverses the longitudinal dimension of the mandrel While the mandrel is rotating.

In accordance with this invention a filament wound vessel is made by winding a plurality of layers of strands or ribbons about a rotating mandrel. Certain of the layers are composed of substantially longitudinal windin s and other layers are formed by using transverse windings. When assembling the vessel, it is advantageous to alternately dispose the dilferent types of windings between each other. Each type of winding is wrapped in a repetitive particular configuration that requires at least one point of intersection to form a single configuration. A point of intersection is defined as any point on the winding comprising the wall, which is in the form of a surface of revolution, of a particular layer at which the winding is wrapped across itself to form the particular configuration. An individual winding is formed after the strands or ribbons have been wrapped about the mandrel the necessary number of times to make the particular configuration. The points of intersection are necessary because the windings of a layer must be wrapped back and forth across the mandrel to form a layer that has adequate strength characteristics in all directions.

In accordance with one aspect of this invention the points of intersection of the windings in a particular layer are out of register with the points of intersection in adjacent layers. This avoids the possibility that uninterrupted passages through the wall could be created with the resultant loss of liquid and gas tightness. Moreover, the misalignment between the points of intersection of individual windings in adjacent layers reduces any excessive bending stresses that might otherwise occur in the filaments which would cause buckling and fracturing of the strands. These stresses would result in local weakening of the wall.

Turning now to the drawings, there are illustrated six exemplary windings that can be used to form the novel filament wound vessel of this invention that has improved strength characteristics. In each instance only one winding of the layer has been represented; however, the particular configuration of the individual winding will bviously be repeated until the layer has been completed. As is conventionally accomplished, the winding of the layer should be carried out so that a pitch corresponding to the width of the ribbons or the diameter of the strands is taken into account so that in each full layer the ribbons or strands are disposed in a compact relaionship alongside each other and are all in a coplanar relationship. FIGURES 4, 8 and 12 only illustrate the widest dimension of the filament wound vessel and have omitted the portions of the single windings illustrated that would otherwise appear in the views because of their smaller diameters. This is intended to highlight the fact that layers formed from the illustrated transverse windings cover only the wall of the vessel that is being formed and do not extend to the poles.

By the term point of return is meant the extent of the traverse of the carriage or the arm that is carrying out the winding. More particularly, the points of return represent the longitudinal extent that must be reached on the mandrel to accomplish the particular configuration of the winding.

FIGURES 1 and 2 illustrate a single winding of a layer that will be of a substantially longitudinal winding. The Type I winding shown is asymmetric or excentric in relation to the meridian X of the mandrel and the eventual filament wound vessel itself. The Type I winding has a point of intersection 11 at one of the poles and is not wound around the other pole so that an opening 12 can be formed to allow the mandrel to be removed from the vessel after it has been wound. Any type of a collapsible or deflatable mandrel may be used. The Type I winding also has points of intersection that are indicated at 13 and 14. These are positioned near the opening 12 and between opening 12 and the meridian X. In this type of winding, one point of return is indicated at 15 and the other point of return coincides with the point of intersection 11, which is located at the opposite pole.

FIGURES 3 and 4 show a transverse winding indicated as Type II. The individual winding has four points of intersection, indicated as 23 and 24, that are located asymmetrically with respect to the meridian X and which leave large openings 22 around the two poles of the vessel that is being formed. The points of return are indicated as 25.

The Type III windings are illustrated in FIGURES 5 and 6 and are substantially longitudinal. The points of intersection are asymmetric in relation to the meridian X and are indicated at 31, 33, 34 and 36. Openings 32 around both of the poles are formed by this type of winding. The points of return are indicated at 35.

FIGURES 7 and 8 illustrate a layer of transverse windings designated as Type IV in which there is only one point of intersection 41 and it falls on the meridian X. The points of return are indicated at 45 with the winding leading to large openings 42 around the poles.

To enable a smooth transition in the actual carrying out of the alternate winding of transverse and substantially longitudinal windings one aspect of this invention provides a conversion layer that has a distance between its points of return intermediate the longer distance of the substantially longitudinal windings and the shorter distance of the transverse windings. Thus, there is illustrated in FIGURES 9 and 10 a winding designated as Type V that has five points of intersection. One intersection 51 is located on the meridian X while points 53 are located between one pole and the meridian and the points 54 are located between the other pole and the meridian. The points of return are indicated at 55 and leave openings 52 around the poles.

The last type of winding, Type VI (FIGURES l1 and 12), illustrates a transverse winding similar to the Type IV winding shown in FIGURES 7 and 8 except that the single point of intersection, indicated at 61, is not located on the meridian X as in Type IV but is located between the meridian and one of the poles of the filament wound vessel. The points of return indicated at 65 are consequently located asymmetrically in relation to the meridian X and two openings 62 of different sizes are left around the poles of the vessel.

FIGURES 13 and 14 illustrate an embodiment of the present invention wherein the substantially longitudinal windings of FIGURE 1 are superimposed upon the transverse windings of FIGURE 3. In accordance with this embodiment, it will be noted that the points of intersection of the superimposed windings are out of register with each other as are the points of return and the point of return of one and the point of intersection of the other. This is in accordance with a preferred embodiment of the present invention.

In accordance with another feature of this invention the filament wound vessel is formed in such a manner that the points of return of a particular layer of windings located on the walls of the filament wound vessel are out of register with the points of intersection of adjacent layers. The creation of passages through the wall and of excessive bending stresses are thereby further avoided. Thus, as can be seen from a comparison of FIGURE 9 with FIGURE 5, Type V windings should not be followed by or preceded by a layer of Type III windings because the points of return 55 of the Type V windings may coincide, or nearly coincide, with the points of intersection 33 of the Type III windings. Another aspect of this inven tion provides that the points of return of a particular layer located on the walls of the filament wound vessel are also out of register with the points of return of adjacent layers. As seen from FIGURES 1 and 2 and FIG- URE 5, the Type I windings should not follow or precede the Type III windings since the point of return 15 of Type I would nearly coincide with point of return 35 of the Type III windings.

In assembling a filament wound vessel from the exemplary types of windings that have been illustrated, a plurality of layers are wound until the desired wall thickness is reached. Eighteen or twenty layers is a typical number for many applications. The particular order of the types of windings that is used Will vary depending upon the strength characteristics desired in the vessel being formed. The usual method is to preselect the order in which the types are to be used and program the winding machine to carry out the selected order.

To select the order it must be remembered that the points of intersection and points of return that will be located on the wall of the filament wound vessel in a particular layer should be out of register with the points of intersection and points of return of adjacent layers. For even if these points nearly coincide localized weak spots on the wall will appear because the excessive bending stresses resulting from an alignment of the points cause rupturing or buckling of the filaments. This is particularly true when the vessel is used as a pressure vessel for housing liquified petroleum gas. These excessive bending stresses occur primarily on the curved surface of the wall of the vessel. The flat portions of the vessel, i.e.those near the poles of the vessel, do not create any substantial bending stresses.

As one arbitrary example, the six exemplary types of windings could be advantageously combined in the following manner:

Layer number: Type of winding 1 I (substantially longitudinal) In developing a program for determining the order in which particular types of windings are to be used, a comparison of the prior layer and the prospective layer will determine whether the prospective layer can follow the prior layer without weakening the wall of the vesel that is being formed. It should be appreciated that it is unnecessary to use all of the six types of windings that have been illustrated in forming a vessel. The illustrated windings are merely exemplary and the important aspect is that the points of intersection and return of one layer are not in register with the points of intersection and return of adjacent layers. In this connection, it is important to note that the points of return of a particular type of winding can be moved toward or away from the poles of the vessel a small distance. This allows points of intersection or return of one layer to be out of register with the points of intersection or return of an adjacent layer rather than nearly coinciding, which would weaken the wall of the vessel.

By the term substantially longitudinal windings is meant that the strands or ribbons are wound in a configuration the extends substantially the entire distance between the poles of the vessel with the windings passing over at least a portion of one of the poles. In contradistinction, the term transverse windings defines strands or ribbons that have been wound so that the configuration does not extend the entire distance of the wall of the filament wound vessel, which is in the form of a surface of revolution. The transverse windings are disposed at an acute angle with respect to the substantially longitudinal windings.

It can thus be seen that the present invention has provided a method for forming a novel filament wound vessel that has improved strength characteristics. The positioning 6 of the layers of the substantially longitudinal filament windings and transverse windings is such that uninterrupted passages through the wall are avoided. Moreover, any excessive bending stresses that might otherwise be present because of the aligned relationship of the points of intersection or points of return of adjacent layers has been minimized by maintaining these points out of register so that the resulting structure is substantially free from any localized weak spots.

I claim as my invention:

1. A filament wound vessel having poles at the longitudinal ends thereof and having a predetermined wall thickness which comprises a first layer of strands of adhesive impregnated filaments wound in a first predeter mined configuration having at least one point of intersection and two points of return, a second layer of strands of adhesive impregnated filaments wound in a second predetermined configuration having at least one point of intersection and two points of return and overlaying said first layer, the points of intersection of said second layer being out of register with the points of intersection of said first layer and suflicient other layers of strands of adhesive impregnated filaments wound in certain predetermined configurations having at least one point of intersection and two points of return overlaying said first two layers to define the predetermined wall thickness, each subsequent layer having its points of intersection out of register with the proceeding layer, the configuration of at least some of the windings being substantially longitudinal and others being transverse, said substantially longitudi nal windings extending substantially the entire distance between said poles of said vessel with said windings passing over at least a portion of one of said poles, and said transverse windings being disposed at an acute angle with respect to the substantial windings and extending less than the entire distance of the wall of said filament wound vessel.

2. The filament wound vessel of claim 1 wherein the points of return of a particular layer are out of register with the points of intersection of the adjacent layers.

3. The filament wound vessel of claim 2 wherein the point of return of a particular layer are out of register with the points of return of adjacent layers.

References Cited UNITED STATES PATENTS 2,747,649 5/1956 Reed 156-175 2,791,241 5/ 1957 Reed.

2,848,133 8/1958 Ra'mberg 2203 3,047,191 7/1962 Young 22083 3,083,864 '4/1963 Young 220-83 3,317,146 5/1967 Holman 242--3 3,144,952 8/1964 Uhlig et a1. 220 -3 3,203,845 8/1965 Short 220-3 XR 3,309,185 3/1967 Weber 156175 XR FOREIGN PATENTS 1,414,309 9/1965 France.

RAPHAEL H. SCHWARTZ, Primary Examiner US. Cl. X.R. 15 6-175 

